Ionothermal synthesis of black Ti3+-doped single-crystal TiO2 as an active photocatalyst for pollutant degradation and H2 generation

Abstract

A black Ti³⁺-doped single-crystal TiO₂ (Ti³⁺/TiO₂) was one-pot synthesized by treating Ti metal in an ionic liquid containing LiAc and HAc under mild ionothermal conditions. The ionic liquid (1-methyl-imidazolium tetrafluoroborate) supplied an environment enriched with fluoride ions for dissolving titanium foil under ionothermal conditions, followed by reducing protons in acetic acid to form Ti³⁺ ions, leading to Ti³⁺-doped single-crystal TiO₂ as a black powder. EPR and XPS results indicated the high concentrations of both Ti³⁺-dopants and oxygen vacancies. The Ti³⁺ incorporated into the TiO₂ lattice could narrow the energy band gap of TiO₂via forming intermediate energy levels, leading to a visible photocatalyst. Meanwhile, the oxygen vacancies could inhibit the photoelectron–hole recombination. As expected, such a black Ti³⁺/TiO₂ exhibited high activity in the photocatalytic degradation of organic pollutants and water splitting for H₂ production under irradiation with visible light and/or simulated solar light.